You really don't want to go with the conversion to a different size bearing such as the SBC 400- - - -that's a project for professional machinists with decades of experience and access to lots of expensive machine tools. Let the machinist who regrinds the crankshaft source rod and main bearings- - - -if he drops the ball, it's on him to make it right. Be sure to get the connecting rods reconditioned when the rest of the machine work is done. Main bearings for the 54 and early 55 235 engines with the dowel pins in the upper bearings are extremely scarce, and expensive. It's possible to modify the engine block to accept the later model main bearings that are more plentiful and less expensive, but it's not a job a shade tree wrench jockey should attempt.

Did you loosen the main bearing caps before putting all that force on the crankshaft? That's "engine disassembly 101".
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!